Discovering cyber-attack process model based on analytical attack graphs

ABSTRACT

Implementations of the present disclosure include receiving analytical attack graph data representative of an analytical attack graph, the analytical attack graph including: one or more rule nodes each representing a network configuration rule; and one or more impact nodes each representing an impact of one or more respective network configuration rules; converting the analytical attack graph to a tactic graph including one or more tactic nodes, each tactic node representing at least one rule node and at least one impact node; determining one or more paths of the tactic graph that lead to a particular network impact; generating a process model based on the paths that lead to the particular network impact, the process model representing network activity for execution of a process that leads to the particular network impact; and executing one or more remedial actions based on the process model to mitigate cyber-security risk to the enterprise network.

BACKGROUND

Enterprises execute operations across one or more networks of components, commonly referred to as computer networks. A computer network is made up of multiple interconnected components that communicate with one another to facilitate execution of enterprise operations. Example components can include computers, servers, database systems, and the like. Enterprise operations can include processes that are executed across multiple components within a network.

Computer networks are susceptible to attack by malicious users (e.g., hackers). For example, hackers can infiltrate computer networks in an effort to obtain sensitive information (e.g., user credentials, payment information, address information, social security numbers) and/or to take over control of one or more systems. To defend against such attacks, enterprises use security systems to monitor occurrences of potentially adverse events occurring within a network, and alert security personnel to such occurrences. For example, one or more dashboards can be provided, which provide lists of alerts that are to be addressed by the security personnel.

An important aspect in mitigating attacks is an understanding of the relationship between an attack process and a path within a network that the attack process occurs over. This can be referred to as cyber-attack process discovery within computer networks. An approach to cyber-attack discovery within computer networks needs to address multiple technical challenges.

SUMMARY

Implementations of the present disclosure are directed to cyber-attack process discovery in computer networks. More particularly, implementations of the present disclosure are directed to automated cyber-attack process discovery in computer networks by processing analytical attack graphs (AAGs) to provide a cyber-attack process model. As described in further detail herein, implementations of the present disclosure can be used to discover a model representing possible attack path types that exist in an AAG. The disclosed implementations can be used to provide simplified, scalable analytical models. Generated process models can be input to cyber security analytical programs for use in security risk evaluation, security risk management, and detection and tracking of in-progress attacks.

In some implementations, actions include receiving analytical attack graph data representative of an analytical attack graph, the analytical attack graph including: one or more rule nodes each representing a network configuration rule; and one or more impact nodes each representing an impact of one or more respective network configuration rules; converting the analytical attack graph to a tactic graph including one or more tactic nodes, each tactic node representing at least one rule node and at least one impact node; determining one or more paths of the tactic graph that lead to a particular network impact; generating a process model based on the one or more paths that lead to the particular network impact, the process model representing network activity for execution of a process that leads to the particular network impact; and executing, within the enterprise network, one or more remedial actions based on the process model to mitigate cyber-security risk to the enterprise network. Other implementations of this aspect include corresponding systems, apparatus, and computer programs, configured to perform the actions of the methods, encoded on computer storage devices.

These and other implementations can each optionally include one or more of the following features. In some implementations, each rule node is associated with a rule type; and each tactic node is associated with a rule type of the respective at least one rule node that is represented by the tactic node.

In some implementations, converting the analytical attack graph to a tactic graph includes: retrieving, from a database, data that associates tactic nodes with combinations of rule nodes and impact nodes; and replacing combinations of rule nodes and impact nodes of the analytical attack graph with tactic nodes based on the retrieved data.

In some implementations, the analytical attack graph includes one or more fact nodes each representing an input condition.

In some implementations, one or more tactic nodes of the tactic graph each represent at least one fact node in combination with the at least one rule node and the at least one impact node.

In some implementations, generating a process model based on the one or more paths that lead to the particular network impact includes: generating, from the tactic graph, an event log, the event log including a plurality of events, each event being associated with a respective path of the one or more paths of the tactic graph.

In some implementations, each event of the event log is associated with a timestamp indicating a time of the event with respect to a simulated start time of the respective path.

In some implementations, the analytical attack graph data is based on simulated security attacks on the enterprise network.

In some implementations, each rule node is associated with a hardness score representing a difficulty of achieving the network configuration rule by an attacker.

In some implementations, the process model includes one or more network activity nodes, and each network activity node corresponds to one or more tactic nodes of the tactic graph.

In some implementations, the one or more tactic nodes corresponding to a network activity node represent rule nodes of the same rule type.

In some implementations, determining one or more paths of the tactic graph that lead to a particular network impact includes determining the one or more paths using a graph traversal algorithm.

In some implementations, the actions include: comparing network traffic of actual execution of processes within the enterprise network to a set of process models, the set of process models including the process model; and identifying the process as being performed in the enterprise network based on the comparing.

In some implementations, the actions include determining, based on a set of process models, a level of security risk of the enterprise network.

In some implementations, the actions include training a machine-learning (ML) model at least partially based on the process model.

The present disclosure also provides a computer-readable storage medium coupled to one or more processors and having instructions stored thereon which, when executed by the one or more processors, cause the one or more processors to perform operations in accordance with implementations of the methods provided herein.

The present disclosure further provides a system for implementing the methods provided herein. The system includes one or more processors, and a computer-readable storage medium coupled to the one or more processors having instructions stored thereon which, when executed by the one or more processors, cause the one or more processors to perform operations in accordance with implementations of the methods provided herein.

It is appreciated that methods in accordance with the present disclosure can include any combination of the aspects and features described herein. That is, methods in accordance with the present disclosure are not limited to the combinations of aspects and features specifically described herein, but also include any combination of the aspects and features provided.

The details of one or more implementations of the present disclosure are set forth in the accompanying drawings and the description below. Other features and advantages of the present disclosure will be apparent from the description and drawings, and from the claims.

DESCRIPTION OF DRAWINGS

FIG. 1 depicts an example architecture that can be used to execute implementations of the present disclosure.

FIG. 2 depicts an example computer network in accordance with implementations of the present disclosure.

FIG. 3 depicts an example conceptual architecture in accordance with implementations of the present disclosure.

FIG. 4 depicts an example portion of an example analytical attack graph (AAG) including multiple attack paths.

FIG. 5 depicts an example transformation of an example AAG to an example tactic graph and an example extraction of attack paths in accordance with implementations of the present disclosure.

FIG. 6 depicts an example transformation of an example tactic graph to an event log in accordance with implementations of the present disclosure.

FIG. 7 depicts example process discovery using an example event log.

FIG. 8 depicts an example process that can be executed in accordance with implementations of the present disclosure.

Like reference symbols in the various drawings indicate like elements.

DETAILED DESCRIPTION

Implementations of the present disclosure are directed to cyber-attack process discovery in computer networks. More particularly, implementations of the present disclosure are directed to automated cyber-attack process discovery in computer networks by processing analytical attack graphs (AAGs) to provide a cyber-attack process model. In some implementations, actions include receiving analytical attack graph data representative of an analytical attack graph, the analytical attack graph including: one or more rule nodes each representing a network configuration rule; and one or more impact nodes each representing an impact of one or more respective network configuration rules; converting the analytical attack graph to a tactic graph including one or more tactic nodes, each tactic node representing at least one rule node and at least one impact node; determining one or more paths of the tactic graph that lead to a particular network impact; generating a process model based on the one or more paths that lead to the particular network impact, the process model representing network activity for execution of a process that leads to the particular network impact; and executing, within the enterprise network, one or more remedial actions based on the process model to mitigate cyber-security risk to the enterprise network.

To provide context for implementations of the present disclosure, and as introduced above, enterprises execute operations across one or more networks of components, commonly referred to as computer networks. A computer network is made up of multiple interconnected components that communicate with one another to facilitate execution of enterprise operations. Example components can include computers, servers, database systems, and the like. Enterprise operations can include processes that are executed across multiple components within a network.

Computer networks are susceptible to attack by malicious users (e.g., hackers). For example, hackers can infiltrate computer networks in an effort to obtain sensitive information (e.g., user credentials, payment information, address information, social security numbers) and/or to take over control of one or more systems. To defend against such attacks, enterprises use security systems to monitor occurrences of potentially adverse events occurring within a network, and alert security personnel to such occurrences. For example, one or more dashboards can be provided, which provide lists of alerts that are to be addressed by the security personnel.

An important aspect in mitigating attacks is an understanding of the relationship between a cyber-attack process and one or more paths within a network that the cyber-attack process occurs over. This can be referred to as cyber-attack process discovery within computer networks. An approach to cyber-attack process discovery within computer networks needs to address multiple technical challenges. Example technical challenges include scalability and technical resources expended for graph processing. For example, AAGs can be provided to represent potential attack paths for a cyber-attack through a computer network. However, the AAGs are relatively large in size, which requires significant bandwidth and processing power for graph-processing of an AAG.

Technical challenges for cyber-attack process discovery can include versatility of the provided graphs. For example, an AAG can represent potential attack paths through a particular computer network. However, the AAG is specific to the particular computer network, and includes configuration items, rules, and facts for the particular computer network. The AAG therefore is generally limited to use in process discovery for the particular network.

Technical challenges for cyber-attack process discovery can also include availability of attack path data. For example, an AAG can be generated using data representing actual attacks that have occurred in computer networks. In some examples, an AAG can be generated using data representing observed attacks that have been performed by a hacker or by programmed bots in computer networks. The AAGs therefore may omit certain activity patterns that correspond to possible attack paths. For example, an attack path that has not yet been performed by a hacker or by an attack bot might not be captured by an AAG. Additionally, generating an AAG based on real-time activity patterns can be time intensive.

Technical challenges for cyber-attack process discovery can also include identifying high priority and low priority attack paths. For example, AAGs can be large in volume and include many attack paths. An AAG might not include information indicating a hardness or difficulty level of each path. Therefore, it can be difficult to prioritize security threats using an AAG.

In view of the above context, implementations of the present disclosure are directed to cyber-attack process discovery in computer networks. More particularly, implementations of the present disclosure are directed to automated cyber-attack process discovery in computer networks by processing AAGs to provide a cyber-attack process model. In general, implementations of the present disclosure address technical challenges, such as those described above, by providing process models that are smaller in size, compared to AAGs. The process models therefore require reduced time, memory, and processing power compared to AAGs.

Implementations of the present disclosure can also address technical challenges, for example, by generating process models based on tactics that can be applied to multiple different computer networks. Therefore, the process models generated according to the present disclosure can have increased versatility and applicability compared to the AAG, as they are not specific to a computer network.

Implementations of the present disclosure can also address technical challenges, for example, by generating process models based on domain knowledge and using inference. An inference engine can consider various configurations, vulnerabilities, privileges, and a set of rules that are inferred to identify possible attack paths. The disclosed processes can include storing information indicating the inferred possible attack paths. The stored information can also include data that associates combinations of rules, impacts, and facts of the attack paths with tactics that can be used to attack the computer network. Therefore, tactics can account for network activity that has not yet been performed by a hacker or an attack bot. As such, the process models generated according to the present disclosure can have increased scope and completeness as compared to the AAGs. The process models can also be generated more quickly, due to not being reliant on real-time monitoring of an attack.

Implementations of the present disclosure can also address technical challenges, for example, by generating process models including attack paths that are encoded with hardness scores. For example, each tactic used to generate the process model can be assigned a hardness score based on the difficulty of the tactic. Therefore, the process models generated according to the present disclosure can have increased contextual information that can be used to prioritize security measures. For example, based on a process model encoded with hardness scores, an analytical service can determine to prioritize implementing security measures an easier attack path over implementing security measures for a more difficult attack path.

To provide further context for implementations of the present disclosure, a computer network is made up of multiple network components, which can be referred to as configuration items (CIs). Example network components can include, without limitation, servers (e.g., web servers, application servers, mail servers, network servers, proxy servers), databases, desktop computers, laptop computers, and the like. Within a computer network, the network components are connected within a network topology. Network components can include information technology (IT) components and operation technology (OT) components. In general, IT components can be described as hardware and/or software for storage, retrieval, transmission, and manipulation of data within a network. In general, OT components can be described as hardware and/or software that detects changes and/or causes changes within a network by the directly monitoring and/or controlling physical devices, processes, and/or events within the network.

FIG. 1 depicts an example architecture 100 in accordance with implementations of the present disclosure. In the depicted example, the example architecture 100 includes a client device 102, a network 106, and a server system 108. The server system 108 includes one or more server devices and databases (e.g., processors, memory). In the depicted example, a user 112 interacts with the client device 102.

In some examples, the client device 102 can communicate with the server system 108 over the network 106. In some examples, the client device 102 includes any appropriate type of computing device such as a desktop computer, a laptop computer, a handheld computer, a tablet computer, a personal digital assistant (PDA), a cellular telephone, a network appliance, a camera, a smart phone, an enhanced general packet radio service (EGPRS) mobile phone, a media player, a navigation device, an email device, a game console, or an appropriate combination of any two or more of these devices or other data processing devices. In some implementations, the network 106 can include a large computer network, such as a local area network (LAN), a wide area network (WAN), the Internet, a cellular network, a telephone network (e.g., PSTN) or an appropriate combination thereof connecting any number of communication devices, mobile computing devices, fixed computing devices and server systems.

In some implementations, the server system 108 includes at least one server and at least one data store. In the example of FIG. 1 , the server system 108 is intended to represent various forms of servers including, but not limited to a web server, an application server, a proxy server, a network server, and/or a server pool. In general, server systems accept requests for application services and provide such services to any number of client devices (e.g., the client device 102 over the network 106). In accordance with implementations of the present disclosure, and as noted above, the server system 108 can host a process discovery platform in accordance with implementations of the present disclosure.

In the example of FIG. 1 , an enterprise network 120 is depicted. The enterprise network 120 represents a computer network implemented by an enterprise to perform its operations. That is, one or more processes that support enterprise operations are executed within the enterprise network 120. In some examples, the enterprise network 120 represents on-premise systems (e.g., local and/or distributed), cloud-based systems, and/or combinations thereof. In some examples, the enterprise network 120 includes IT components and OT components. In general, IT components include hardware (e.g., computing devices, servers, computers, mobile devices) and software used to store, retrieve, transmit, and/or manipulate data within the enterprise network 120. In general, OT components include hardware and software used to monitor and detect or cause changes in processes within the enterprise network 120. In some examples, the enterprise network 120 includes multiple assets (e.g., CIs). Example assets include, without limitation, users 122, computing devices 124, electronic documents 126, and servers 128.

In some implementations, the cyber-attack process discovery platform of the present disclosure is hosted within the server system 108. As described in further detail herein, the cyber-attack process discovery platform processes AAGs to provide a cyber-attack process model for each cyber-attack process that can be executed within the enterprise network 120. The cyber-attack process model can be described as a pattern that generically represents execution of a cyber-attack process within the enterprise network 120. In some examples, the cyber-attack process model can be represented in a graph structure. Example graph structures can include, but are not limited to, a petri-net and a causal-net.

In accordance with implementations of the present disclosure, the cyber-attack process models can be stored in a graph database and serve as source to an analytical service. Each cyber-attack process model can represent possible attack path types that exist in the enterprise network 120 in a manner that enables simplified visualization and scalable analytics.

The cyber-attack process model can be a compact model of the cyber-attack process and can enable the analytical service to perform a number of actions. For example, the analytical service can train a machine-learning (ML) model at least partially based on the process model. For example, the analytical service can use the process model train a ML model to recognize network activity that corresponds to potential enterprise network attacks.

The analytical service can use cyber-attack process models to calculate a security risk level for the enterprise network 120. Due to decreased size and processing power requirements, a security risk level of an enterprise network 120 can be determined more quickly, and updated more quickly, using the process models compared to using the AAGs. The calculated security risk level of the enterprise network 120 can be used as a basis for modifying security postures and access requirements of the enterprise network 120.

The analytical service can use cyber-attack process models for predictive monitoring of the enterprise network 120. For example, given that at least a first step of a process model has occurred, the analytical service can identify the step(s) as being part of an attack path of a process model, and can predict the next step to be performed by the attacker. The analytical service can then perform security actions to prevent the attacker from progressing along the attack path.

FIG. 2 depicts an example portion 200 of a computer network. The example portion 200 graphically represents a network topology of an enterprise network. In some examples, the computer network is graphically represented as nodes 202, 204, 206, 208 and edges 210, 212, 214 between nodes. In some examples, each edge can be associated with a respective session representing communication between nodes. While the example portion 200 of the computer network includes relatively few nodes, it is contemplated that a computer network can include hundreds, or thousands of nodes.

Implementations of the automated cyber-attack process discovery of the present disclosure are described in further detail herein with reference to FIGS. 3-7 . FIG. 3 depicts an example conceptual architecture 300 in accordance with implementations of the present disclosure. FIG. 4 depicts an example portion of an example AAG 400 including multiple attack paths. FIG. 5 depicts an example transformation of an example AAG 502 to an example tactic graph 504 in accordance with implementations of the present disclosure. FIG. 6 depicts an example transformation of the example tactic graph 504 to an event log 602 in accordance with implementations of the present disclosure. FIG. 7 depicts example process discovery using the example event log 602.

With particular reference to FIG. 3 , the conceptual architecture 300 includes a process discovery platform 302 and an analytical service 304. As described in further detail herein, the process discovery platform 302 performs automated process discovery to provide a set of process models. Each process model can represent a possible attack process that can be implemented in an enterprise network. In some examples, each process model can be represented in a graph structure. Example graph structures can include, but are not limited to, a dependency flow graph, a petri-net, and a causal-net.

In further detail, and in the example of FIG. 3 , the process discovery platform 302 includes a tactic graph converter 308, a path extractor 310, an event log converter 312, and a process discovery module 314. The process discovery platform 302 further includes a graph database 306.

In some examples, the graph database 306 can store AAGs for one or more enterprise networks. The AAGs can be generated, for example, using an inference engine that can consider various configurations, vulnerabilities, privileges, and set of rules that are inferred to identify possible attack paths. The inference engine can generate attack paths for simulated security attacks on the network. The simulated security attacks can simulate sequences of possible actions performed by an attacker. The graph database 306 can store data representing the inferred possible attack paths of the AAGs.

FIG. 4 depicts an example portion 400 of an example AAG to illustrate implementations of the present disclosure. As depicted in the example of FIG. 4 , the AAG can include different node types to show how a set of network and system configurations result in unauthorized actions to specific targets. The example portion 400 is depicted in a database structure (e.g., Neo4j graph database structure). Nodes in an AAG are of different types: circular nodes representing system or network configurations that are the conditions (also referred to as facts) that provide possibilities for actions by an attacker; hexagonal nodes representing reasoning rules that represent the attack methodology leveraged by an attacker to achieve a particular goal; and square nodes that represent an impact as a sub-goal for a certain action an attacker could take. The AAG includes two types of edges: configuration-to-rule edges that represent logical AND (i.e., all configuration conditions have to be true to cause the impact); and rule-to-impact edges that represent logical OR (i.e., the impact happens if at least one rule is satisfied).

In general, the AAG is created by taking into account the configurations directed by some rules in order to make some impacts on the target network. In some examples, all configuration nodes, impact nodes, and rule nodes can be provided in sets N_(p), N_(d), N_(r), respectively. Accordingly, N_(p)={n_(p,j)|n_(p,j)∈V, ∀n_(p,j) is a configuration}, N_(d)={n_(d,j)|n_(d,j)∈V, ∀n_(d,j) is an impact}, and N_(r)={n_(r,j)|n_(r,j)∈V, ∀n_(r,j) is a rule}. Consequently, the combination of these sets accounts for all vertices of the graph.

Rule nodes can be associated with a hardness score. The hardness score of a rule can represent a measure of difficulty of achieving the rule by an attacker. The hardness score can be, for example, a score having a value between zero and one. The hardness score can be set as an attribute of an outgoing edge of a rule. Other edges can be assigned a hardness score of zero. In some examples, the hardness score is specified by domain experts. In some examples, the hardness score is embedded within the ontology according to rule type. Rule nodes can also be associated with a rule type. The rule type can be set as a property of each rule.

In some examples, a configuration node is referred to herein as an input fact node indicating facts that are provided as input within a configuration. In some examples, impact nodes are referred to herein as derived fact nodes indicating a derived fact that results from applying one or more input facts and/or one or more derived facts to a rule.

AAGs can be used in cyber-threat analysis to determine attack paths of external attackers into and through a computer network. Use of AAGs in mitigating attacks on computer networks is described in further detail in commonly assigned U.S. application Ser. No. 16/554,846, entitled Generating Attack Graphs in Agile Security Platforms, and filed on Aug. 29, 2019, the disclosure of which is expressly incorporated herein by reference in the entirety for all purposes. Further, generation of AAGs is described in further detail in commonly assigned U.S. application Ser. No. 16/924,483, entitled Resource-efficient Generation of Analytical Attack Graphs, and filed on Jul. 9, 2020, the disclosure of which is expressly incorporated herein by reference in the entirety for all purposes.

With continued reference to FIG. 4 , the example portion 400 is spread across a first configuration item (CI₁) and a second configuration item (CI₂), and each attack path 402, 404, starts from fact nodes (input conditions) 406, 408 to a derived fact node represented as an impact (I₁) 414. Each attack path 402, 404 respectively progresses from the fact nodes 406, 408 through derived fact nodes (impacts) based on rules to the impact (I₁) 414. However, the attack path 404 is also dependent on fact nodes 410, 412.

In the example of FIG. 4 , the attack path 402 (first attack path) is represented as P_(x)={I₆, I₅, I₂, I₁}, and the attack path 404 (second attack path) is represented as P_(y)={I₆, I₄, I₃I₂, I₁}. Progression along the attack paths 402, 404 can be abstracted as progressions between steps (S). In the example of FIG. 4 , depicted steps include S={S₁, S₂, S₃, S₄, S₅, S₆, S₇}. In some examples, the steps correspond to movement within a physical attach graph (PAG) of the underlying enterprise network.

In the example of FIG. 4 , a process risk for a particular process is to be determined, where the second configuration item (CI₂) is wholly attributed with execution of the process. That is, the first configuration item (CI₁) does not execute any portion of the process, for which a process risk is to be determined. However, the first configuration item (CI₁) is along attack paths to the second configuration item (CI₂). Consequently, and in this non-limiting example, example CI−1 pairs can be provided as: CI₂−I₁, CI₂−I₂, and CI₂−I₃, each of I₁, I₂, and I₃ being achievable in CI₂.

In the example of FIG. 4 , a single path is provided to I₁, which includes evaluating rule R₁ with I₂, a single path is provided to I₃, which includes evaluating R₃ with I₄ and other facts represented by fact nodes 420, 422, and multiple paths are provided to I₂, which includes evaluating R₇ with I₃, or evaluating R₂ with I₅ and another fact represented by a fact node 424.

Referring again to FIG. 3 , and in some examples, the tactic graph converter 308 transforms an AAG to a tactic graph. The path extractor 310 can extract attack paths from the tactic graph. FIG. 5 depicts an example transformation of an example AAG 502 to an example tactic graph 504 by the tactic graph converter 308. FIG. 5 also depicts an example extraction of attack paths from the tactic graph 504 by the path extractor 310.

The example AAG 502 includes two attack paths, where an adversary may perform 3 different types of rules (rule type A, rule type B, rule type C) to reach impact 123 of the computer network.

In the AAG 502, each attack path is represented as an AAG subgraph. A first subgraph includes F₁, R₁₁, I₁₂, R₁₂, and I₂₃. A second subgraph includes F₁, R₂₁, I₂₁, R₂₂, I₂₂, F₂, R₂₃, and I₂₃. Thus, as shown in AAG 502, rule types A and B are each instantiated twice along, while rule type C is instantiated once.

In some examples, the tactic graph converter 308 can convert the AAG 502 to the tactic graph 504 using a set of conversion rules. In some examples, the conversion rules associate combinations of facts, rules, and impacts with tactics. For example, a conversion rule may specify that a combination of rule R₂₁ and impact I₂₁ corresponds to tactic T₂₁. In some examples, the conversion rules can be pre-programmed based on human input. For example, a user can analyze various rules, facts, and impacts to identify patterns of tactics. As an example, a user can determine that an attacker can use tactic T₂₂ to achieve rule R₂₂ to reach impact I₂₂.

In some examples, tactic nodes of a tactic graph can represent at least one fact node in combination with a rule node, an impact node, or both. For example, a user can determine that given an initial condition specified by fact F₂, an attacker can use tactic T₂₃ to achieve rule R₂₃ to reach impact I₂₃.

In some examples, the tactic graph converter 308 can retrieve, from a database, data that associates tactic nodes with combinations of rule nodes, impact nodes, and/or fact nodes. The tactic graph converter 308 can replace combinations of rule nodes, impact nodes, and fact nodes of the analytical attack graph with tactic nodes based on the retrieved data.

In some examples, each tactic can be assigned a rule type. In some examples, each tactic node is associated with the rule type of the respective rule node or nodes that are represented by the tactic node. For example, tactic node T₂₁ can be associated with rule type A as a result of rule node R₂₁ being associated with rule type A, and rule node R₂₁ being represented by tactic node T₂₁ in the tactic graph.

Facts, rules, and impacts of each tactic are represented in the tactic graph within a tactic node, rather than as separated nodes. Each node of the tactic graph 504 represents a tactic that can be performed in a computer network. The tactic graph 504 reflects the sequential order of the attack path. For example, T₁₁ represents an attack tactic that enables an adversary to perform the next attack tactic of T₁₂.

In the tactic graph 504, each attack path is represented as a tactic graph subgraph. A first subgraph includes T₁₁ and T₁₂. A second subgraph includes T₂₁, T₂₂, and T₂₃. Thus, as shown in tactic graph 504, and consistent with AAG 502, tactics of rule types A and B are each instantiated twice along, while rule type C is instantiated once. For example, T₁₁ and T₂₁ have the same rule type of rule type A. This indicates that the same type of tactic can be executed on two different hosts in a simulated attack pattern.

Representation of attack paths in a tactic graph can enable retrieval of attack paths using graph traversal algorithms. For example, the path extractor 310 can use graph traversal algorithms to determine one or more paths of the tactic graph 504 that lead to a particular network impact (e.g., an attack goal represented by I₂₃).

In some examples, the path extractor 310 can extract paths from the tactic graph 504 using a breadth-first search (BFS) algorithm. In some examples, the path extractor 310 can extract paths from the tactic graph 504 using a depth-first search (DFS) algorithm.

In some examples, the path extractor 310 can extract paths from the tactic graph 504 using a k shortest path algorithm. When using a k shortest path algorithm, the path extractor 310 can use hardness scores as relationship weights. In some examples, the path extractor 310 can extract paths from the tactic graph 504 using a random walk algorithm.

The path extractor 310 extracts two attack paths from the tactic graph 504. A first path P₁ includes T₁₁ and T₁₂. A second path P₂ includes T₂₁, T₂₂, and T₂₃.

In some examples, the event log converter 312 can convert the paths to an event log. FIG. 6 depicts an example transformation of an example tactic graph to an event log in accordance with implementations of the present disclosure. For example, the event log converter 312 can generate, from the paths P₁ and P₂, an event log 602. The event log 602 includes a series of events. Each event of the event log 602 is associated with a path extracted from the tactic graph 504.

The event log 602 can be a log of simulated events according to the extensible event stream (XES) format. Each event of the event log 602 refers to a case, an activity, and a point in time. In the example of FIG. 6 , each event of the event log includes refers to a case that corresponds to a path, an activity that corresponds to a rule type, and a point in time that corresponds to a timestamp with reference to a simulated start time of the respective attack path.

FIG. 7 depicts example process discovery using an example event log. For example, the process discovery module 314 can perform process discovery using the event log 602. In some examples, the process discovery module 314 can perform process discovery using a direct flows graph. In some examples, the process discovery module 314 can perform process discovery using an inductive miner algorithm. In some examples, the process discovery module 314 can perform process discovery using a heuristic miner algorithm.

The process discovery module 314 generates a process model 702 including multiple network activity nodes. Each network activity node in the process model 702 represents one or more tactics associated with a particular rule type. For example, network activity node A of the process model 702 represents tactic T₁₁ and tactic T₂₁. Both tactic T₁₁ and tactic T₂₁ represent rules of rule type A. Thus, tactic T₁₁ and tactic T₂₁ are included in different paths of the tactic graph 504, yet are combined into a same network activity node A of the process model 702.

Each edge in the process model 702 can represent a possible transition between two network activity nodes. For example, each edge can represent a possible usage of two or more tactics of an attack path. Each edge can have multiple properties. For example, each edge can have a property of transition frequency, probability, and hardness score.

In the examples illustrated in FIGS. 5 to 7 , the number of graph nodes is reduced from eleven to five, while preserving key features of calculating analytics according to the described usages. Process model 702 can be considered a compact representation of an AAG, encoded with frequencies and probabilities of various attack paths.

The process model 702 can be stored in the graph database 306. Process models of the graph database can be provided to an analytical service 304. The analytical service 304 can compare network activity to process models of the graph database 305 to perform network security functions. For example, the analytical service 304 can use the process models to determine a security risk level of the network, to identify and predict network attacks, to prevent network attacks, etc.

For example, the analytical service 304 can monitor and track network activity within an enterprise network. The analytical service 304 can compare the network activity to process models of the graph database 305. Based on the comparison, the analytical service 304 may determine that the process defined by a process model (e.g., the process model 702) is being performed in the enterprise network or has been performed in the enterprise network.

For example, the analytical service 304 may determine that a tactic of rule type A has been performed in the enterprise network. Therefore, the analytical service 304 can determine that the process represented by the process model 702 is likely in progress, and that the attacker is likely going to perform a tactic of rule type B. In response to determining that an attack is in progress, the analytical service 304 can perform action such as increasing an assigned security risk level of the computer network, restricting access to certain network components, generating an alert, etc.

With regard to detecting cyber-attacks on a live computer network, network traffic patterns can be collected during enterprise operations. One or more network traffic patterns can be compared to process models within a set of process models, each process model in the set of process models being generated by the process discovery platform of the present disclosure, as described herein. In some examples, if a network traffic pattern is determined to sufficiently match a process model, the network traffic pattern can be determined to correspond to the process associated with the process model.

To detect cyber-attacks on a live computer network, the analytical service 304 can compare observed behavior of the network to the generated process models. The observed behavior of the network can include network traffic events or any other events captured by data collection platforms, e.g., as represented by cases of an event log.

Comparing the observed behavior to the process models can include performing a conformance check that measures one or more conformance statistics. Results of the conformance check can indicate whether the observed behavior matches the process model, identify where deviations occur, and indicate how severely the observed behavior does not comply the process model.

Conformance statistics can include, for example, a log-model fitness and a precision of the observed behavior according to the process model. A process model with good fitness allows for most or all of the behavior of the event log. A process model with good precision does not allow for much more behavior than what is included in the event log.

Fitness of the observed behavior can be calculated, for example, by constructing alignments among each case observed in an event log of observed behavior to a process model's petri net. Fitness between the event log and the process model can then be determined as an average of cases fitness across all event log cases. Another approach to calculating fitness uses token-based replay to calculate fitness. The token-based replay approach matches an event log case to a petri net process model to discover which transitions are executed and in which places there are remaining or missing tokens for the given case.

Precision of the observed behavior can be calculated, for example, by transforming a process model's petri net to a transition system. For each event, an amount of observed behavior in the event log and its allowed behavior according to a transition system can be determined. Precision can be calculated as a ratio between a summarization of observed behaviors across all events of the event log and a summarization of allowed behaviors across all events according to the transition system.

If the conformance statistics, e.g., fitness and precision, are above a threshold fitness and precision, the analytical service 304 can determine that the observed behavior satisfies criteria for matching the process model. Based on determining that the observed behavior satisfies criteria for matching the process model, the analytical service 304 can determine that the observed behavior corresponds to potential attacker behavior as defined in the process model.

With regard to supporting ML approaches, the process models generated in accordance with implementations of the present disclosure can be used as training data to train one or more ML models. For example, one or more ML models can be used to monitor network traffic and perform certain functionality (e.g., alert to anomalous activity, identify instances of processes being executed within a network). That is, for example, an ML model can receive network traffic as input, process the network traffic, and provide output (e.g., an alert indicating anomalous activity and/or an instance of process execution). To enable this, the ML model is trained using training data. In this case, the training data can include processes and respective process models. For example, each process model is labeled with a respective process that it represents to provide labeled training data for supervised learning of the ML model.

In general, a ML model is iteratively trained, where, during an iteration, one or more parameters of the ML model are adjusted, and an output is generated based on the training data. For each iteration, a loss value is determined based on a loss function. The loss value represents a degree of accuracy of the output of the ML model. The loss value can be described as a representation of a degree of difference between the output of the ML model and an expected output of the ML model (the expected output being provided from training data). In some examples, if the loss value does not meet an expected value (e.g., is not equal to zero), parameters of the ML model are adjusted in another iteration of training. In some instances, this process is repeated until the loss value meets the expected value.

In some examples, in response to determining that the process (i.e., an attack) is being performed in the enterprise network or has been performed in the enterprise network, one or more remedial actions can be taken based on the process model to mitigate cyber-security risk to the enterprise network. Example remedial actions can include, without limitation, a remedial action that increases the difficulty (hardness) in achieving an impact, and a remedial action that entirely removes an impact from being achieved. For example, software can be updated (e.g., patched) to obviate a security loophole in a previous version of the software. As another example, access to a configuration item can be (temporarily) blocked to inhibit completion of the process (e.g., a configuration item that is along the process represented in the process model).

FIG. 8 depicts an example process 800 that can be executed in accordance with implementations of the present disclosure. In some implementations, the example process 800 may be performed using one or more computer-executable programs executed using one or more computing devices. In some examples, the example process 800 can be executed for each of one or more processes executed during enterprise operations to provide an attack process model for each attack.

The process 800 includes obtaining an AAG (802). For example, and as described herein, the tactic graph converter 308 can obtain the AAG 502 from the graph database 306. The process 800 includes converting the AAG to a tactic graph (804). For example, and as described herein, the tactic graph converter 308 can transform the AAG 502 to the tactic graph 504. Each tactic of the tactic graph 504 can represent a combination of rules, impacts, facts, or any of these.

The process 800 includes extracting attack paths from the tactic graph (806). For example, and as described herein, the path extractor 310 can extract paths P1 and P2 from the tactic graph 504. The process 800 includes converting attack paths to an event log (808). For example, and as described herein, the event log converter 312 can convert the paths P1 and P2 to the event log 602.

The process 800 includes generating a process model from the event log (810). For example, and as described herein, the process discovery module 314 can generate a process model 702 from the event log 602. The process model 702 can be provided to an analytical service 304 for use in analyzing a security posture of an enterprise network and guarding against cyber-attacks on the enterprise network.

Implementations and all of the functional operations described in this specification may be realized in digital electronic circuitry, or in computer software, firmware, or hardware, including the structures disclosed in this specification and their structural equivalents, or in combinations of one or more of them. Implementations may be realized as one or more computer program products (i.e., one or more modules of computer program instructions encoded on a computer readable medium for execution by, or to control the operation of, data processing apparatus). The computer readable medium may be a machine-readable storage device, a machine-readable storage substrate, a memory device, a composition of matter effecting a machine-readable propagated signal, or a combination of one or more of them. The term “computing system” encompasses all apparatus, devices, and machines for processing data, including by way of example a programmable processor, a computer, or multiple processors or computers. The apparatus may include, in addition to hardware, code that creates an execution environment for the computer program in question (e.g., code) that constitutes processor firmware, a protocol stack, a database management system, an operating system, or a combination of one or more of them. A propagated signal is an artificially generated signal (e.g., a machine-generated electrical, optical, or electromagnetic signal) that is generated to encode information for transmission to suitable receiver apparatus.

A computer program (also known as a program, software, software application, script, or code) may be written in any appropriate form of programming language, including compiled or interpreted languages, and it may be deployed in any appropriate form, including as a stand-alone program or as a module, component, subroutine, or other unit suitable for use in a computing environment. A computer program does not necessarily correspond to a file in a file system. A program may be stored in a portion of a file that holds other programs or data (e.g., one or more scripts stored in a markup language document), in a single file dedicated to the program in question, or in multiple coordinated files (e.g., files that store one or more modules, sub programs, or portions of code). A computer program may be deployed to be executed on one computer or on multiple computers that are located at one site or distributed across multiple sites and interconnected by a communication network.

The processes and logic flows described in this specification may be performed by one or more programmable processors executing one or more computer programs to perform functions by operating on input data and generating output. The processes and logic flows may also be performed by, and apparatus may also be implemented as, special purpose logic circuitry (e.g., an FPGA (field programmable gate array) or an ASIC (application specific integrated circuit)).

Processors suitable for the execution of a computer program include, by way of example, both general and special purpose microprocessors, and any one or more processors of any appropriate kind of digital computer. Generally, a processor will receive instructions and data from a read only memory or a random access memory or both. Elements of a computer can include a processor for performing instructions and one or more memory devices for storing instructions and data. Generally, a computer will also include, or be operatively coupled to receive data from or transfer data to, or both, one or more mass storage devices for storing data (e.g., magnetic, magneto optical disks, or optical disks). However, a computer need not have such devices. Moreover, a computer may be embedded in another device (e.g., a mobile telephone, a personal digital assistant (PDA), a mobile audio player, a Global Positioning System (GPS) receiver). Computer readable media suitable for storing computer program instructions and data include all forms of non-volatile memory, media and memory devices, including by way of example semiconductor memory devices (e.g., EPROM, EEPROM, and flash memory devices); magnetic disks (e.g., internal hard disks or removable disks); magneto optical disks; and CD ROM and DVD-ROM disks. The processor and the memory may be supplemented by, or incorporated in, special purpose logic circuitry.

To provide for interaction with a user, implementations may be realized on a computer having a display device (e.g., a CRT (cathode ray tube), LCD (liquid crystal display), LED (light-emitting diode) monitor, for displaying information to the user and a keyboard and a pointing device (e.g., a mouse or a trackball), by which the user may provide input to the computer. Other kinds of devices may be used to provide for interaction with a user as well; for example, feedback provided to the user may be any appropriate form of sensory feedback (e.g., visual feedback, auditory feedback, or tactile feedback); and input from the user may be received in any appropriate form, including acoustic, speech, or tactile input.

Implementations may be realized in a computing system that includes a back end component (e.g., as a data server), or that includes a middleware component (e.g., an application server), or that includes a front end component (e.g., a client computer having a graphical user interface or a Web browser through which a user may interact with an implementation), or any appropriate combination of one or more such back end, middleware, or front end components. The components of the system may be interconnected by any appropriate form or medium of digital data communication (e.g., a communication network). Examples of communication networks include a local area network (“LAN”) and a wide area network (“WAN”) (e.g., the Internet).

The computing system may include clients and servers. A client and server are generally remote from each other and typically interact through a communication network. The relationship of client and server arises by virtue of computer programs running on the respective computers and having a client-server relationship to each other.

While this specification contains many specifics, these should not be construed as limitations on the scope of the disclosure or of what may be claimed, but rather as descriptions of features specific to particular implementations. Certain features that are described in this specification in the context of separate implementations may also be implemented in combination in a single implementation. Conversely, various features that are described in the context of a single implementation may also be implemented in multiple implementations separately or in any suitable sub-combination. Moreover, although features may be described above as acting in certain combinations and even initially claimed as such, one or more features from a claimed combination may in some cases be excised from the combination, and the claimed combination may be directed to a sub-combination or variation of a sub-combination.

Similarly, while operations are depicted in the drawings in a particular order, this should not be understood as requiring that such operations be performed in the particular order shown or in sequential order, or that all illustrated operations be performed, to achieve desirable results. In certain circumstances, multitasking and parallel processing may be advantageous. Moreover, the separation of various system components in the implementations described above should not be understood as requiring such separation in all implementations, and it should be understood that the described program components and systems may generally be integrated together in a single software product or packaged into multiple software products.

A number of implementations have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the disclosure. For example, various forms of the flows shown above may be used, with steps re-ordered, added, or removed. Accordingly, other implementations are within the scope of the following claims. 

What is claimed is:
 1. A computer-implemented method for security of an enterprise network, comprising: receiving analytical attack graph data representative of an analytical attack graph, the analytical attack graph including: one or more rule nodes each representing a network configuration rule; and one or more impact nodes each representing an impact of one or more respective network configuration rules; converting the analytical attack graph to a tactic graph including one or more tactic nodes, each tactic node representing at least one rule node and at least one impact node; determining one or more paths of the tactic graph that lead to a particular network impact; generating a process model based on the one or more paths that lead to the particular network impact, the process model representing network activity for execution of a process that leads to the particular network impact; and executing, within the enterprise network, one or more remedial actions based on the process model to mitigate cyber-security risk to the enterprise network.
 2. The method of claim 1, wherein: each rule node is associated with a rule type; and each tactic node is associated with a rule type of the respective at least one rule node that is represented by the tactic node.
 3. The method of claim 1, wherein converting the analytical attack graph to a tactic graph includes: retrieving, from a database, data that associates tactic nodes with combinations of rule nodes and impact nodes; and replacing combinations of rule nodes and impact nodes of the analytical attack graph with tactic nodes based on the retrieved data.
 4. The method of claim 1, wherein the analytical attack graph includes one or more fact nodes each representing an input condition.
 5. The method of claim 4, wherein one or more tactic nodes of the tactic graph each represent at least one fact node in combination with the at least one rule node and the at least one impact node.
 6. The method of claim 1, wherein generating a process model based on the one or more paths that lead to the particular network impact comprises: generating, from the tactic graph, an event log, the event log including a plurality of events, each event being associated with a respective path of the one or more paths of the tactic graph.
 7. The method of claim 6, wherein each event of the event log is associated with a timestamp indicating a time of the event with respect to a simulated start time of the respective path.
 8. The method of claim 1, wherein the analytical attack graph data is based on simulated security attacks on the enterprise network.
 9. The method of claim 1, wherein each rule node is associated with a hardness score representing a difficulty of achieving the network configuration rule by an attacker.
 10. The method of claim 1, wherein: the process model includes one or more network activity nodes, and each network activity node corresponds to one or more tactic nodes of the tactic graph.
 11. The method of claim 10, wherein the one or more tactic nodes corresponding to a network activity node represent rule nodes of the same rule type.
 12. The method of claim 1, wherein determining one or more paths of the tactic graph that lead to a particular network impact includes determining the one or more paths using a graph traversal algorithm.
 13. The method of claim 1, further comprising: comparing network traffic of actual execution of processes within the enterprise network to a set of process models, the set of process models comprising the process model; and identifying the process as being performed in the enterprise network based on the comparing.
 14. The method of claim 1, further comprising determining, based on a set of process models, a level of security risk of the enterprise network.
 15. The method of claim 1, further comprising training a machine-learning (ML) model at least partially based on the process model.
 16. A non-transitory computer-readable storage medium coupled to one or more processors and having instructions stored thereon which, when executed by the one or more processors, cause the one or more processors to perform operations for process discovery in a computer network based on session traffic, the operations comprising: receiving analytical attack graph data representative of an analytical attack graph, the analytical attack graph including: one or more rule nodes each representing a network configuration rule; and one or more impact nodes each representing an impact of one or more respective network configuration rules; converting the analytical attack graph to a tactic graph including one or more tactic nodes, each tactic node representing at least one rule node and at least one impact node; determining one or more paths of the tactic graph that lead to a particular network impact; generating a process model based on the one or more paths that lead to the particular network impact, the process model representing network activity for execution of a process that leads to the particular network impact; and executing, within the enterprise network, one or more remedial actions based on the process model to mitigate cyber-security risk to the enterprise network.
 17. The non-transitory computer-readable storage medium of claim 16, wherein: each rule node is associated with a rule type; and each tactic node is associated with a rule type of the respective at least one rule node that is represented by the tactic node.
 18. The non-transitory computer-readable storage medium of claim 16, wherein converting the analytical attack graph to a tactic graph includes: retrieving, from a database, data that associates tactic nodes with combinations of rule nodes and impact nodes; and replacing combinations of rule nodes and impact nodes of the analytical attack graph with tactic nodes based on the retrieved data.
 19. The non-transitory computer-readable storage medium of claim 16, wherein the analytical attack graph includes one or more fact nodes each representing an input condition.
 20. A system, comprising: one or more computers; and a computer-readable storage device coupled to the one or more computers and having instructions stored thereon which, when executed by the one or more computers, cause the one or more computers to perform operations for process discovery in a computer network based on session traffic, the operations comprising: receiving analytical attack graph data representative of an analytical attack graph, the analytical attack graph including: one or more rule nodes each representing a network configuration rule; and one or more impact nodes each representing an impact of one or more respective network configuration rules; converting the analytical attack graph to a tactic graph including one or more tactic nodes, each tactic node representing at least one rule node and at least one impact node; determining one or more paths of the tactic graph that lead to a particular network impact; generating a process model based on the one or more paths that lead to the particular network impact, the process model representing network activity for execution of a process that leads to the particular network impact; and executing, within the enterprise network, one or more remedial actions based on the process model to mitigate cyber-security risk to the enterprise network. 